Many individuals are dissatisfied with their current tooth color. Thus, there is a desire for whiter teeth which can be achieved through the use of tooth whitening products. The whitening effect can be effected by chemically altering or removing the stain and/or changing the visual perception of the color of the teeth is known in the literature that the visual perception of a white substance can be altered through the deposition of an optical brightener, blue pigment or blue dye, especially one for which the hue angle (in the CIELAB scale) of the reflected or emitted light is between 200 to 320 degrees. This effect is commonly used in laundry detergent products to make white clothes appear “whiter” to the human eye. The same concept has been applied to tooth whitening as well. The natural off-white or yellow color of teeth can be made to appear whiter through the deposition of a blue substance onto teeth. Using pigments with a deposition aid, such as Gantrez® (copolymers of maleic anhydride and with methyl vinylether) in toothpaste to make teeth look whiter is disclosed in EP1935395B1.
It has been demonstrated in EP1935395 that the deposition of the blue substance from aqueous solutions onto teeth is optimal if the blue substance has limited solubility in saliva as is the case with a blue pigment. In addition, it was shown that the deposition is optimal if a high molecular weight polymer (MW>200,000 Da) such as Gantrez type polymers, PEGs, and cellulose ethers was present in the formulation to help the pigment adhere to the tooth. It is also known that other polymers, specifically low molecular weight hydroxypropylmethylcellulose polymers, can increase the deposition of blue pigment on teeth especially when the blue pigment is encapsulated within the matrix of a strip of the polymer.
Dyes have significantly different properties than pigments, in particular, dyes are much more soluble in water than pigments. This solubility of dyes makes them much more difficult to deposit and be retained on teeth. U.S. Pat. No. 6,030,222 discloses depositing dyes on teeth when blended with specific carriers. US Patent Application Publication 2012/0093905 discloses dyes coupled to certain polymers.
Blue dye, such as FD&C blue #1 or FD&C blue #5, is of a different chemical structure than blue pigment 15 so has a different solubility in water. In fact, the solubility of FD&C Blue #1 dye is >20 g/100 mL in water, as compared to <0.1 g/100 ml for blue pigment 15. The greater solubility of blue dye in water as compared to blue pigment will logically make it more difficult to deposit and retain blue dye on teeth in the hydrated environment of the oral cavity. To increase the deposition of blue dye Unilever has filed a patent application in which they covalently attach blue dye to a polymer backbone (US2012/0093905 A1). Luster White Now markets a toothpaste which claims to instantly whiten teeth in which a PVM/MA Copolymer is included in the formulation to presumably increase the retention of FD&C Blue #1 on teeth. Another granted patent (U.S. Pat. No. 6,030,222) claims to increase tooth-whitening through the absorption of blue dye into the pores of teeth, preferable from a hydrophilic carrier which aids absorption of the complementary dyes into the aqueous environment surrounding the teeth.
It would be desirable to have tooth whitening oral care products containing dyes that can produce superior temporary tooth whitening effects when incorporated into oral care products.